I've been pondering this problem for a while. I don't know the right way to publish versions. The problem is that you really have to publish the version for every module in order to know what's going on. We can (and eventually will) track version numbers for each module, but right now we have no centralized way of storing this information.
I think that the easiest way to actually know what versions they're running is to figure out what day they got the code from CVS, because we can always figure it out from a datestamp (even though sf's anon cvs trails behind, we can get pretty close).
